Many types of knee joints for orthotic and prosthetic devices are commonly available on the market. The most rudimentary joints do not allow knee flexion during active tasks such as walking and can be manually unlocked for tasks such as sitting. This type of joint does not help restore the natural dynamics of a healthy leg.
More advanced joints use mechanical design or electronic control allowing to automatically, albeit abruptly, switch between a locked state and an unlocked state of the knee hinge. This offers stability during the stance phase and flexion during the swing phase. However, because the transitions between the locked and unlocked states are not smoothly controlled, the natural dynamics of a healthy leg is not restored.
None of the commonly available orthosis knee joints on the market, and only a few prosthetic knees, allow the users to descend inclines and stairs because of the absence of controlled flexion during the stance phase.
Among the different technologies that are being used or could be used for actively controlling orthotic and prosthetic knee hinges, few are desirable. For example, an electric motor and gear set incorporated in an actuated hinge could provide the required torque and motion control, but is likely to be noisy, heavy and bulky.
Actuation systems incorporating controlled resistance hydraulic actuators such as the C-Leg® from Otto Bock have the ability to provide some level of motion control. However, these systems are difficult to package on orthotic devices due to the size of the components and to the mechanical arrangement of those parts on the leg support system.
Other technologies such as the active muscle assistance device developed by Tibion look promising. However, the motor requires a transmission system in order to provide the required torque and incorporating a transmission to the control system adds design complexity, weight and size to the solution.
The magnetorheological (MR) Damper technology utilized in the Rheo Knee™ from Ossur demonstrates excellent controllability and provides a good torque density, although not sufficient for an orthotic application.
Ideally, the actuation technology utilized on a controllable orthotic or prosthetic knee hinge would provide a good level of control and torque capacity while being light, compact, easy to integrate on the leg support system and operate silently.
Therefore there is a need for a controllable actuation system having high torque density, allowing a user to descend inclines stairs, while being compact enough to properly fitting on a leg support system.